The present invention relates to a method of producing monolayered or multilayered composite materials consisting of ceramic and metal, ceramic and ceramic, or the like, and more particularly, to a method of producing functionally gradient materials with properties varying continuously in the direction of the thickness by adjusting the distribution of components and the structure thereof through the synthesis effected by a self-propagating reaction of the mixed fine particles including constitutive elements of these ceramics and metals, etc.
One of the recent important technological themes in the fields of aeronautics, space engineering, and the nuclear fusion reactor, etc., is the development of a super heat-resistant material with superior heat-blocking properties, and that of a heat-blocking material to be used in a light-weight aircraft. As the producing method of such a heat-blocking material, there is conventionally known the method of coating the surface of a metal and an alloy with ceramics or the like; for example, the surface of a Ni-base super alloy is coated with MCrAlY (wherein, M is a metal) as a relaxation layer and ZrO.sub.2.Y.sub.2 O.sub.3 in this order according to a plasma-coating method. Furthermore, an ion-plating method wherein a heat-blocking material is fixed by impact on a substrate by vaporization under a vacuum of 10.sup.-2 to 10.sup.-3 Torr; a plasma-CVD (Chemical Vapor Deposition) method wherein a heat-blocking material is formed by vapor-phase synthesis; and an ion-beam method have been used frequently.
However, these conventional methods, i.e. the plasma coating method, ion-plating method, plasma-CVD method and ion-beam method are defective because of low efficiency, since much time is required to form a thick coating because the coating layer obtained per an unit time is very thin. Such a defect is revealed more remarkably as the surface area of the substrate to be coated becomes larger. Furthermore, there is another defect in that the ion-plating method and the plasma-CVD method require a large-scale chamber and additional equipment, and the plasma-coating method requires a large amount of energy to heat and fuse the coating material.
Though the monlayered or the multilayered coating obtained by the above methods should naturally be superior in adhesion and against a thermal stress, none of the composite materials provided by these conventional coating or plating method has been proved to have a stress relaxing structure based on a theoretical calculation. The structure of such materials have been obtained by merely varying the composition thereof stepwise and does not have superior adhesion, since the compositional distribution and temperature gradient in such materials are not controlled, in the producing process, to be continuous so that the structure may exhibit minimum thermal stress distribution corresponding to a temperature potential at each portion of the material under working conditions.
Accordingly, these composite materials have problems such as exfoliation of the coating layer due to the thermal stress caused repeatedly during operation and the variation by the passage of time, and the deterioration of corrosion resistance due to the generation of cracks.